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Aquatic Species at Risk - Rocky Mountain Ridged Mussel

Rocky Mountain Ridged Mussel

Image reproduced with permission from the Canadian Museum of Nature, Ottawa, Canada.

SARA Status: Special ConcernCOSEWIC Status: Endangered

Region: British Columbia

Did You Know?

After drifting passively until they contact a suitable host fish, larvae attach to its gills or fins and remain for approximately one to six weeks while transforming into a juvenile mussel. As juveniles, they drop off the fish and begin a free-living benthic life.

Table of Contents

Description

The Rocky Mountain Ridged mussel is a large freshwater mussel. Its typically thin shell is trapezoidal and up to 12.5 cm long and 0.4 cm wide. Like that of all other mussels, the shell of this species is composed of two parts, known as valves, connected by a hinge. The hinge is medium-sized and has small, irregular, indistinct anterior teeth. The surface of the shell is marked by well-defined growth rings, and the dorsal valve is distinguished by a sharp, prominent ridge at the beak. For juveniles, the outside of the shell is greenish or ochre, while adults are typically darker, becoming bluish-black. The inside of the shell is white tinged with coppery blue. From counts of annual growth rings on the shells, it is believed Rocky Mountain Ridged mussels can live up to about 30 years.

Habitat

Globally, this freshwater species occurs from southern British Columbia to southern California; and eastward to southern Idaho and northern Nevada in the United States. In Canada, they are limited to the Okanagan basin in southern British Columbia, which represents less than 5% of the global distribution. Records for this species have been verified within valley-bottom water bodies including, from north to south, Okanagan Lake, Skaha Lake, Okanagan River, Vaseux Lake, Park Rill Creek (a tributary of the Okanagan River) and Osoyoos Lake.

The Rocky Mountain Ridged mussel lives in fresh water. It is found in various sizes of lakes and streams with constant flow and in a variety of substrates; in the Okanagan basin it has been found in large cobble, gravel and sandy openings, muddy sediments with sparse vegetation, cobble and gravel over sand, and areas where sediment became turbid when disturbed. They have been found in areas without aquatic vegetation and in areas where low-lying vegetation was interspersed among individual mussels. They are found in shallow water, but could also be in deeper water. They seem to prefer areas with stable habitat conditions and appear to avoid areas with shifting substrates, periodic dewatering, extreme water level fluctuations, seasonal low oxygen levels or murky, nutrient-rich water. This mussel will attach itself to gravel or firm mud on the bottom if it also contains a small amount of fine material such as sand or clay. The mussel may bury itself partially or completely dependent upon substrate type and temperature. It is not unusual to see individuals of all non-larval age classes together at a single location.

Threats

The Rocky Mountain Ridged mussel is threatened by the destruction and degradation of its habitat. Like all members of this family of mussels, it is highly sensitive to changes in its environment, such as those affecting the temperature or composition of the water. Additionally, because mussels filter large volumes of water in order to feed, they are susceptible to dissolved pollutants building up in their bodies. Currently, the introduction and proliferation of exotic species such as Zebra and Quagga mussels is the most serious potential threat to the Rocky Mountain Ridged mussel, as these invasive species can take over habitat, compete for food resources and smother native species.

Further Information

Several achievements contributing to the management of the Rocky Mountain Ridged mussel have been realized in recent years. For example in 2011, the Province of British Columbia and the Department of Fisheries and Oceans Canada cooperatively generated a SARA Management Plan for the species.

As of 2014, the following activities underway include:

the evaluation of a predictive model to identify mussel locations;

continuing surveys to find the species, including deep water surveys;

determining reproductive timing;

assessing mussel migration and age-class distribution;

preliminary work on determining the host fish;

distributing mussel information pamphlets to dive shops, marinas, all levels of government and resource professionals;

incorporating mussel considerations into the Okanagan River flow management tool;

reviewing efficacy of the mussel detection and relocation protocol in use in the Okanagan;

training on field identification of mussels to qualified professionals;

incorporating known mussel areas into the Okanagan Large Lakes Protocol (which guides development activities);

incorporating known areas of mussels into Eurasian Water Milfoil rototilling treatment plans so that the mussels can be avoided;

and, occurrences of invasive mussels are reported to the Province of British Columbia’s Invasive Species Database.

The Rocky Mountain Ridged mussel is listed as Special Concern under the federal Species at Risk Act (SARA). If a project is subject to an assessment under the Canadian Environmental Assessment Act, 2012 measures must be taken to avoid or lessen any adverse effects of the project on the species. More information about SARA, including how it protects individual species, is available on the Species at Risk Public Registry.